According to the CDC, COVID-19 spreads when an infected person breathes out droplets and very small particles that contain the virus. These droplets and particles can be breathed in by other people or land on their eyes, noses, or mouth. In some circumstances, they may contaminate surfaces they touch.

It is now generally accepted that the main form of transmission is airborne, and that the virus can travel distances beyond 1.8m (for example, during choir practice, in restaurants, or in fitness classes). In general, indoor environments without good ventilation increase this risk.

Respiratory droplets and small particles can also land on surfaces. Other people can become infected with the virus by touching these objects or surfaces, then touching their eyes, nose or mouth, although this is less common.

Well-designed and maintained HVAC systems can help control the spread of COVID-19.

The WHO recommends increasing outdoor air ventilation using initiatives such as economy cycles, and avoiding recirculation of air. Building owners and operators should seek qualified advice on increasing ventilation in existing systems.

In line with guidance from SafeWork Australia, AIRAH recommends that employers seek confirmation from their building owner or facilities manager that the air conditioning system is properly designed and maintained.

Keeping relative humidity between 40 and 60 per cent will create conditions that reduce the risk of infection through inhalation of airborne droplets carrying the virus. Research from the International Society of Indoor Air Quality and Climate (ISIAQ) shows that viruses survive better at increased humidity with 60 per cent active above 60 per cent relative humidity.

Low humidity in occupied buildings should be avoided as this can dry out the mucous membrane which is one of our primary means of defence. ISIAQ research shows that virus survival decreases with decreasing humidity.

The WHO recommends increasing air filtration to as high as possible without significantly diminishing design airflow. AIRAH strongly advises seeking qualified advice that effective air filters at the recommended performance level have been selected and maintained appropriately.

The suite of resources and advisory notes developed by A.G. Coombs provides excellent advice on many aspects of COVID-19 and HVAC systems.

This interview with the chair of ASHRAE's Epidemic Task Force, William Bahnfleth, contains useful information about the effectiveness of filters, UV and other HVAC technologies in controlling COVID-19.

The WHO has also provided specific advice on the use of fans. It notes that table or pedestal fans are safe for air circulation among family members living together who are not infected with the virus. However, fans should be avoided when people who are not part of the immediate family are visiting, since some people could have the virus despite not having symptoms. Air blowing from an infected person directly at another in closed spaces may increase the transmission of the virus from one person to another.

The typical split-system air conditioning units common in Australia also circulate air within a room. As indicated above, care should be taken to avoid situations where air from an infected person may be blown directly onto other people.

Please note that some ventilation systems, such as those in carparks, do not recirculate – all air is exhausted directly to the atmosphere. These systems are therefore highly unlikely to spread the virus unless they feed into nearby air intakes for other HVAC systems.

As the COVID-19 pandemic has progressed, many products have been heavily marketed to provide air cleaning. These include ionisation, dry hydrogen peroxide, and chemical fogging disinfection, as well as combinations of these technologies.

AIRAH does not provide recommendations for, or against, any manufacturer or product, and supports the advice of the CDC with regard to emerging technologies:

“While variations of these technologies have been around for decades, relative to other air cleaning or disinfection methods, they have a less-documented track record when it comes to cleaning/disinfecting large and fast volumes of moving air within HVAC systems or even inside individual rooms. This does not necessarily imply the technologies do not work as advertised. However, in the absence of an established body of peer-reviewed evidence showing proven efficacy and safety under as-used conditions, the technologies are still considered by many to be ‘emerging’.

“As with all emerging technologies, consumers are encouraged to exercise caution and to do their homework. Registration alone, with national or local authorities, does not always imply product efficacy or safety. Consumers should research the technology, attempting to match any specific claims against the intended use of the product. Consumers should request testing data that quantitively demonstrates a clear protective benefit and occupant safety under conditions consistent with the intended use. When considering air cleaning technologies that potentially or intentionally expose building occupants, the safety data should be applicable to all occupants, including those with health conditions that could be aggravated by the air treatment. In transient spaces, where average exposures to the public may be temporary, it is important to also consider occupational exposures for workers that must spend prolonged periods in the space.

“Preferably, the documented performance data under as-used conditions should be available from multiple sources, some of which should be independent, third-party sources. Unsubstantiated claims of performance or limited case studies with only one device in one room and no reference controls should be questioned. At a minimum, when considering the acquisition and use of products with technology that may generate ozone, verify that the equipment meets UL 867 standard certification (Standard for Electrostatic Air Cleaners) for production of acceptable levels of ozone, or preferably UL 2998 standard certification (Environmental Claim Validation Procedure (ECVP) for Zero Ozone Emissions from Air Cleaners) which is intended to validate that no ozone is produced.”

It is sensible to address HVAC characteristics by specifying HVAC requirements in a brief to property consultants. Because buildings and their HVAC arrangements are unique, the characteristics of installed HVAC systems like ventilation, filtration, relative pressures and HVAC hygiene can only be determined by inspection or audit by a specialist.

Often air conditioning services are specified in lease agreements in terms of indoor temperature achieved and hours of access. Characteristics such as ventilation, filtration and HVAC hygiene are left to minimum standards like the National Construction Code, or building ratings systems.

Some of the characteristics to keep in mind:

• Ventilation – Outdoor air rates need to be minimum (AS 1668.2 generally 10 L/s/person) or better. Higher ventilation rates can lead to higher energy use without heat exchange and correct control.
• Ventilation effectiveness – Some HVAC arrangements (e.g., underfloor air distribution) are more successful at reducing infection exposure than others. Once-through systems provide more protection than recirculating systems.
• Filtration – Filters should be selected with the highest possible efficiency (ISOePM1 efficiency to ISO16890.2016 and/or ≥EN779.2012 F7 or ASHRAE52.2.2017 MERV13-A), within the operational and design parameters of the HVAC system. AIRAH strongly advises seeking qualified advice that effective air filters at the recommended performance level have been selected and maintained appropriately.
• UV treatment – In-duct or on-coil systems are options, but need to be engineered correctly and maintained.
• Maintenance – A very important and often ignored factor. How often are the filters changed, outdoor air rates checked, ducts and coils inspected/cleaned?
• Air pathways – A primary concern, particularly in multi-tenanted buildings, is air pathways. Does air flow the way it has been designed? How are outdoor air intake ventilation and spill or exhaust air quantities balanced? How well air-separated are tenancies from each other? Recirculation may be a concern, if other occupancies share a common ventilation system. Ventilation (and other) arrangements in shared areas such as corridors, lobbies and lifts are also of interest. Relative pressures between spaces will determine where air actually flows.
• Humidity control – An important element that is often not well addressed in air conditioning. While all refrigerated air conditioning systems will act to de-humidify the air being cooled, controlling humidity within specified limits is really only addressed in premium leases or specialised applications such as health, manufacturing and data centres.

Again, each building and HVAC system is unique, and AIRAH recommends consulting an HVAC&R specialist.

There is no indication at this stage that home air conditioning systems can spread the disease. Although AIRAH recommends regular maintenance and cleaning of air conditioning equipment, there is no special cleaning or disinfecting requirement because of the coronavirus.

If you suspect that the surface of an air conditioning unit has been affected – by someone coughing on it, for example – use a simple disinfectant similar to that recommended by the United States Environmental Protection Agency to clean the surface.

Please note, however, that the typical split-system air conditioning units common in Australia circulate the air within a room, much like fans. As indicated above, care should be taken to avoid situations where air from an infected person may be blown directly onto other people.

Evaporative air conditioning systems use drinking water. According to the Water Services Association of Australia (WSAA), drinking water in Australia is high quality and is well treated. There is no evidence that drinking water will be affected by the COVID-19 virus or that it is transmitted by drinking water. Existing water treatment and disinfection processes, including use of chlorine, are effective in removing viruses from water supplies. The WSAA has developed a public fact sheet for customers around water and COVID-19.

According to the Centres for Disease Control and Prevention (CDC), there is currently no evidence to support transmission of COVID-19 associated with food. It says that “there is likely very low risk of spread from food products or packaging that are shipped over a period of days or weeks at ambient, refrigerated, or frozen temperatures”.

The CDC says that before preparing or eating food it is important to always wash your hands with soap and water for 20 seconds for general food safety. It also recommends washing your hands throughout the day after blowing your nose, coughing or sneezing, or going to the bathroom.

According to the WHO, some planes have cabin air filtration systems equipped with HEPA filters which can remove viruses and germs quickly, minimising the duration of the exposure to any potential infectious materials produced by a cough or sneeze. The cabin air system is designed to operate most efficiently by delivering approximately 50 per cent outside air and 50 per cent filtered, recirculated air. The air supply is essentially sterile and particle-free. However, adequate ventilation is just one of the preventive measures to reduce the risk of COVID-19 transmission. Other important measures include maintaining physical distance of at least 1.5 metres whenever possible, frequent hand hygiene and wearing a mask. Passengers should check with the airline company and the national or local guidelines about when and where to wear a mask while flying.

For the latest advice on wearing masks, refer to the Australian Department of Health and World Health Organization websites.

AIRAH recommends that HVAC&R professionals conducting essential work, especially in areas with community transmission of COVID-19, remain informed about the latest recommendations and consider the use of masks where appropriate.

Health experts have recommended wearing a tight-fitting mask with efficient filtration such as an N95, KN95 or KF94 mask, which can filter out at least 95 per cent of airborne particles, according to the Centers for Disease Control and Prevention.

According to the WHO, coronaviruses (including preliminary information on the COVID-19 virus) may persist on surfaces for a few hours or up to several days. This may vary under different conditions (e.g., type of surface, temperature or humidity of the environment).

The WHO recommends cleaning surfaces that may be affected then treating with simple disinfectant to destroy the virus and protect yourself and others. Wash your hands regularly with soap and water or an alcohol-based hand rub. Avoid touching your eyes, mouth, or nose.